The Silverlight 2 platform exposes the limitation of calling the TransformToVisual method from an element that is not in the main visual tree. Now this is a real problem especially for RadWindow because the window is not in the main visual tree. RadWindow is displayed in Popup control and the visual tree of the popup is not connected to the main visual tree (the main visual tree is the tree from Application.Current.RootVisual).

Solution:

The general recommendation is to open RadWindow after the Loaded event has been fired.

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